Kash Younas, a taxi driver, of Ferriston, Banbury said it had been made clear to staff at the Horton A&E department that his mother, Kaniz Aziz, could speak very little English and did not have a mobile phone.
The Oxford University Hospitals NHS Trust is investigating the incident.
Mrs Aziz, 68, was taken to the Horton on January 5 at 12pm with severe pain in her shoulder and arm. Because of Covid rules her daughter-in-law was not allowed to stay with her and returned home. Mr Younas said she was assured by the receptionist that an interpreter would be provided.
"My sister in law gave two different mobile numbers and they had a number on the system as next of kin, which is myself, so one of us could pick her up. But that wasn't the case. She was discharged without anyone being informed," said Mr Younas.
"My mother suffers from bad rheumatoid arthritis; she has difficulty walking and she had a bad shoulder. She walked from the hospital to Ferriston - a very long way in her condition with unsuitable footwear and the weather was bitterly cold. She had no money and can't use a mobile phone."
Mr Younas said his brother went to the hospital in search of his mother but was told she had been discharged. Concerned, he called his wife to ask her to drive through the streets in search of Mrs Aziz, but she could not be found. They returned to the hospital where they were told incorrectly that she had been collected by family members. Mr Younas' brother called 999 to report the elderly lady walking home alone.
At around 3.40pm Mrs Aziz arrived home 'very cold and confused'. Mr Younas described the situation as a 'safeguarding issue' that should not have happened.
"I would like to know what went wrong and why we weren't called to arrange collection of my mother. This is well below the professional standard of care given to a person who has various illnesses by the NHS," he said.
"My brother and I are taxi drivers and collecting her would not have been a problem but unfortunately we never received a call."
Mr Younas said when he complained to the Patient Advice and Liaison Service (PALS) he received a phone call but described the manner of the assistant as 'very rude' when he explained his mother could not speak English well and that he would have to be her advocate. He claims the caller put the phone down on him.
A spokesman for the Oxford University Hospitals NHS Trust said: "The Trust is investigating but has no comment to make at this stage."